1. Field of the Invention
The invention relates to a drilling tool with an interchangeable conveying spiral which is axially secured by means of a supporting device positively supported on the drill shank.
2. Discussion of the Prior Art
Attachable conveying spirals are known, for example, from German Offenlegungsschrift No. 2,543,578 or German Offenlegungsschrift 3,044,775 (U.S. Pat. No. 4,393,947). In the first mentioned specification, the conveying spiral is axially secured by means of a two piece clamping ring which can be fastened to the shank by means of screws. A further annular element is arranged between the circumference of the clamping ring and the circumference of the shank, and a further elastic member which acts as a cushion is arranged between the rear end of the spiral and the clamping ring. Therefore at least four different components are necessary in the object of this supporting device, and assembling or dismantling for exchanging the spiral is complicated. Moreover, the conveying spiral can be axially secured effectively only by extremely careful assembly.
In the embodiment of an axial supporting device according to the additionally quoted German Offenlegungsschrift No. 3,044,775, (U.S. Pat. No. 4,393,947) the conveying spiral, strictly speaking, is not axially secured at all, for the supporting devices defining the conveying spiral are primarily made as centering rings of rubber or plastic. When the conveying spiral is subjected to axial loading, such a component cannot axially secure the conveying spiral effectively.
In a further known device for axially securing a telescopic conveying spiral, a sleeve is used which can be axially displaced against the thrust of the spiral and, in the manner of a feather key, fixes the axial position of a part which positively interacts with the drill shank and the sleeve.